1USERSPACE MAD ACCESS
2 3Device files
4 5 Each port of each InfiniBand device has a "umad" device and an
6 "issm" device attached. For example, a two-port HCA will have two
7 umad devices and two issm devices, while a switch will have one
8 device of each type (for switch port 0).
9 10Creating MAD agents
11 12 A MAD agent can be created by filling in a struct ib_user_mad_reg_req
13 and then calling the IB_USER_MAD_REGISTER_AGENT ioctl on a file
14 descriptor for the appropriate device file. If the registration
15 request succeeds, a 32-bit id will be returned in the structure.
16 For example:
17 18 struct ib_user_mad_reg_req req = { /* ... */ };
19 ret = ioctl(fd, IB_USER_MAD_REGISTER_AGENT, (char *) &req);
20 if (!ret)
21 my_agent = req.id;
22 else
23 perror("agent register");
24 25 Agents can be unregistered with the IB_USER_MAD_UNREGISTER_AGENT
26 ioctl. Also, all agents registered through a file descriptor will
27 be unregistered when the descriptor is closed.
28 29Receiving MADs
30 31 MADs are received using read(). The receive side now supports
32 RMPP. The buffer passed to read() must be at least one
33 struct ib_user_mad + 256 bytes. For example:
34 35 If the buffer passed is not large enough to hold the received
36 MAD (RMPP), the errno is set to ENOSPC and the length of the
37 buffer needed is set in mad.length.
38 39 Example for normal MAD (non RMPP) reads:
40 struct ib_user_mad *mad;
41 mad = malloc(sizeof *mad + 256);
42 ret = read(fd, mad, sizeof *mad + 256);
43 if (ret != sizeof mad + 256) {
44 perror("read");
45 free(mad);
46 }
47 48 Example for RMPP reads:
49 struct ib_user_mad *mad;
50 mad = malloc(sizeof *mad + 256);
51 ret = read(fd, mad, sizeof *mad + 256);
52 if (ret == -ENOSPC)) {
53 length = mad.length;
54 free(mad);
55 mad = malloc(sizeof *mad + length);
56 ret = read(fd, mad, sizeof *mad + length);
57 }
58 if (ret < 0) {
59 perror("read");
60 free(mad);
61 }
62 63 In addition to the actual MAD contents, the other struct ib_user_mad
64 fields will be filled in with information on the received MAD. For
65 example, the remote LID will be in mad.lid.
66 67 If a send times out, a receive will be generated with mad.status set
68 to ETIMEDOUT. Otherwise when a MAD has been successfully received,
69 mad.status will be 0.
70 71 poll()/select() may be used to wait until a MAD can be read.
72 73Sending MADs
74 75 MADs are sent using write(). The agent ID for sending should be
76 filled into the id field of the MAD, the destination LID should be
77 filled into the lid field, and so on. The send side does support
78 RMPP so arbitrary length MAD can be sent. For example:
79 80 struct ib_user_mad *mad;
81 82 mad = malloc(sizeof *mad + mad_length);
83 84 /* fill in mad->data */
85 86 mad->hdr.id = my_agent; /* req.id from agent registration */
87 mad->hdr.lid = my_dest; /* in network byte order... */
88 /* etc. */
89 90 ret = write(fd, &mad, sizeof *mad + mad_length);
91 if (ret != sizeof *mad + mad_length)
92 perror("write");
93 94Transaction IDs
95 96 Users of the umad devices can use the lower 32 bits of the
97 transaction ID field (that is, the least significant half of the
98 field in network byte order) in MADs being sent to match
99 request/response pairs. The upper 32 bits are reserved for use by
100 the kernel and will be overwritten before a MAD is sent.
101 102P_Key Index Handling
103 104 The old ib_umad interface did not allow setting the P_Key index for
105 MADs that are sent and did not provide a way for obtaining the P_Key
106 index of received MADs. A new layout for struct ib_user_mad_hdr
107 with a pkey_index member has been defined; however, to preserve
108 binary compatibility with older applications, this new layout will
109 not be used unless the IB_USER_MAD_ENABLE_PKEY ioctl is called
110 before a file descriptor is used for anything else.
111 112 In September 2008, the IB_USER_MAD_ABI_VERSION will be incremented
113 to 6, the new layout of struct ib_user_mad_hdr will be used by
114 default, and the IB_USER_MAD_ENABLE_PKEY ioctl will be removed.
115 116Setting IsSM Capability Bit
117 118 To set the IsSM capability bit for a port, simply open the
119 corresponding issm device file. If the IsSM bit is already set,
120 then the open call will block until the bit is cleared (or return
121 immediately with errno set to EAGAIN if the O_NONBLOCK flag is
122 passed to open()). The IsSM bit will be cleared when the issm file
123 is closed. No read, write or other operations can be performed on
124 the issm file.
125 126/dev files
127 128 To create the appropriate character device files automatically with
129 udev, a rule like
130 131 KERNEL=="umad*", NAME="infiniband/%k"
132 KERNEL=="issm*", NAME="infiniband/%k"
133 134 can be used. This will create device nodes named
135 136 /dev/infiniband/umad0
137 /dev/infiniband/issm0
138 139 for the first port, and so on. The InfiniBand device and port
140 associated with these devices can be determined from the files
141 142 /sys/class/infiniband_mad/umad0/ibdev
143 /sys/class/infiniband_mad/umad0/port
144 145 and
146 147 /sys/class/infiniband_mad/issm0/ibdev
148 /sys/class/infiniband_mad/issm0/port
149